Recently, to reduce fuel consumption and harmful exhaust gas components, various control methods have been proposed for purposes such as improving the control accuracy of a fuel injection amount and fuel injection timing and improving the control accuracy of ignition timing. Furthermore, for example, approach using a new combustion method such as a method using spark ignition and compression ignition has also been taken. What is requested for further improvement of the control accuracy and proposing a new control method is to accurately grasp a combustion state of an air-fuel mixture made of a fuel and air in a cylinder. Therefore, to accurately grasp the combustion state, it is desirable to detect combustion pressure caused by combustion in the cylinder.
For this reason, there is generally proposed a method in which a hole communicating with a combustion chamber is formed in a cylinder block or a cylinder head, and combustion pressure in a cylinder is applied to a pressure sensing element via the hole to detect the combustion pressure. In this method, an air column vibration that occurs in the hole is an error cause. To suppress the air column vibration that occurs in the hole, it is necessary to shorten the hole. As a result, the pressure sensing element is located near the combustion chamber. Since a thermal shock is large near the combustion chamber, a load on the pressure detection element is large. This is a cause of a failure such as a decrease in sensitivity and disconnection and becomes a technical problem.
Under such circumstances, for example, JP 2006-336498 A (PTL 1) has proposed that a combustion state is detected using an existing crank angle sensor and applied for controlling an internal combustion engine. It is generally known to use a crank angle detection sensor for detecting a crank angular velocity of the internal combustion engine as a means for grasping the combustion state in the cylinder of the internal combustion engine. This crank angle sensor is for detecting the crank angular velocity of the crankshaft of the internal combustion engine, but indirectly detects the combustion state in the combustion chamber and detects a change in the angular velocity of the crankshaft due to a change in the combustion state.
Then, PTL 1 proposes to correct a variation in the cycle of the angle signal of the crank angle sensor and detect the combustion state by properly analyzing the cycle of the angle signal of the crank angle sensor.